1. Field of the Invention
The present invention generally relates to cooling a computer system. More particularly, the present invention relates to a technique for cooling a computer while reducing fan noise. Still more particularly, the invention relates to the use of throttling capabilities in a computer to dynamically select a thermal solution which is quieter than other thermal solutions.
2. Background Information
Computer systems include numerous electrical components that draw electrical current to perform their intended functions. A computer's microprocessor or central processing unit (“CPU”) requires electrical current to perform many functions such as controlling the overall operations of the computer system and performing various numerical calculations. Any electrical device through which electrical current flows produces heat. The amount of heat any one device generates generally is a function of the amount of current flowing through the device.
Typically, each manufacturer designs its products to operate correctly within a predetermined temperature range. If the temperature exceeds the predetermined range (i.e., the device becomes too hot or too cold), the device may not function correctly thereby potentially degrading the overall performance of the computer system. Thus, it is desirable for a computer system generally, and its components specifically, to operate within a thermally benign environment.
A conventional computer system includes one or more fans to blow air over the electronics to keep the electronics cool. A fan's ability to cool a computer is a function of the volume and speed of the airflow it is able to create. Faster fans generally provide greater cooling ability than slower fans. Fans, however, also make noise and the noise level is a function of the speed of the fan; faster are noisier than slower fans.
In some computers, the fan is turned when the computer is turned on and spun at a predetermined speed until the computer is turned off. Although satisfactory for cooling purposes, this approach results in the fan continuously making a great deal of noise, which is generally annoying to the operator. In other computers, to reduce fan noise, the fan is activated upon boot up the fan is activated to a relatively slow speed and only spun faster if it is determined (using a thermal sensor) that the computer has become hotter. Once an increase in temperature is detected, the fan speed is increased. This approach recognizes that a computer that has just booted up and does not yet generate much heat does not need its fan to spin at its higher speed. Such a computer may include one or more temperature sensors that are monitored to determine the thermal state of the computer. If it is determined that the computer is becoming too hot, the fan's speed can be increased. Although this disadvantageously increases the sound level of the computer, it is a necessary action to keep the computer from over heating. Moreover, it is important to keep the computer (e.g., the microprocessor) from becoming so hot that it functions unsafely or unreliably. To prevent unreliable operation, the fan speed is increased with an increase in temperature even though the temperature has not yet reached a critical level. Ramping up fan speed before a critical temperature is reached is generally necessary to head off a thermal problem from occurring.
Early microprocessors dissipated a couple of watts of energy. Today's microprocessors dissipate tens of watts (e.g., 60 watts). Because computers have become more and more powerful, they also have become hotter, thereby requiring a cooling system that can handle the increased thermal loads. This requirement generally has meant making the fans larger, adding additional fans, and/or making the fans spin faster. The sound level of computer cooling systems therefore has increased making the noise problem more severe. As a result, there is a tremendous need to provide a cooling system for a computer that minimizes the sound level of the fans as much as possible. These two design goals are generally at odds with each other—a fan capable of keeping a computer sufficiently cool generates a great deal of noise and a quiet fan may be unable to sufficiently cool the computer, all else being equal. Accordingly, there is a need to provide a cooling system for a computer that effectively trades off system cooling and fan noise.